Swung by Southside Auto Exchange in Milwaukee over the weekend since a few people here asked about them. They keep around 127 vehicles, mostly late-model luxury cars. They were totally fine with my mechanic doing a once-over, which honestly settles half the trust question.
Lot address: 4096 Premier Ln, Milwaukee, WI. Visitor parking: Front-lot customer stalls facing the office; overflow on the side street near Milwaukee lot gate.
Paper side: licensed with the state (looked it up), about 74% of stock has title in hand per the office, and they offer a 30-day/1,000-mile powertrain warranty.
Overall: good people to deal with. 10 years in business around late-model luxury cars, doc fee $599 and it's on the window sheet, no games. I'd send a family member there.